Experiments described in this proposal will determine the mechanism by which the abundant phagocyte protein calprotectin inhibits S. aureus growth. Our preliminary results suggest that upon infection with S. aureus, calprotectin is expressed in kidney and liver abscesses in a neutrophil-dependent manner, but its expression in the heart is neutrophil-independent. We hypothesize that different phagocytic cells distribute calprotectin throughout the body during infection, and the anti-staphylococcal activity of calprotectin is due to this protein's ability to chelate distinct divalent cations. To test this hypothesis, we will determine if calprotectin inhibits staphylococcal growth by hijacking metals away from S. aureus and directly measure the affinity of calprotectin for several divalent cations. To characterize the response of S. aureus to calprotectin, we will define the alterations in staphylococcal gene and protein expression that occur upon calprotectin exposure. Finally, we will determine the contribution of calprotectin to tissue-specific protection against staphylococcal infection by applying advanced proteomic techniques to animal models of infection. The Specific Aims of this proposal are: 1. Determine the contribution of Mn2+ and Zn2+ binding to calprotectin-mediated growth inhibition. 2. Define the S. aureus response to calprotectin exposure. 3. Elucidate the pathophysiologic consequence of the calprotectin-S. aureus interaction. Staphylococcus aureus is a significant human pathogen that is responsible for a wide variety of diseases including impetigo, cellulitis, food poisoning, toxic shock syndrome and sepsis. In addition, this bacterium is the leading cause of nosocomial infections and is becoming increasingly resistant to all known antimicrobials. The experiments in this proposal will enhance our limited knowledge of how bacterial pathogens evade the innate immune response, and may identify novel staphylococcal targets for therapeutic intervention and vaccine development. [unreadable] [unreadable] [unreadable]